1. Field of the Disclosure
Embodiments of the present disclosure relate to a wireless power transmission system, and in particular, relates to a wireless power transmission system compatible with a plurality of transmission methods.
2. Description of the Related Art
In recent years, a wireless power transmission system that wirelessly transmits electric power from a power transmitting device to a power receiving device using magnetic field coupling between a power transmitting coil and a power receiving coil has been put to practical use.
As the transmission method for electric power (hereinafter, abbreviated as a transmission method), which utilizes the magnetic field coupling, an electromagnetic induction method in which the power transmitting coil and the power receiving coil are situated close to each other and electric power is transmitted from the power transmitting device to the power receiving device using electromagnetic induction between the power transmitting coil and the power receiving coil, a magnetic resonance method in which electric power can be transmitted from the power transmitting device to the power receiving device using magnetic resonance between the power transmitting coil and the power receiving coil even if the power transmitting coil and the power receiving coil are separated from each other by a distance, or the like is used.
As a device relating to a wireless power transmission system of the related art based on the electromagnetic induction method, such a non-contact power transfer device (a wireless power transmission system) as illustrated in Japanese Unexamined Patent Application Publication No. 2002-101578 and so forth have been proposed. FIG. 9 is an explanatory diagram illustrating the configuration of a non-contact power transfer device 200 according to Japanese Unexamined Patent Application Publication No. 2002-101578.
As illustrated in FIG. 9, the non-contact power transfer device 200 includes a primary-side circuit corresponding to the power transmitting device and a secondary-side circuit corresponding to the power receiving device. The primary-side circuit includes a direct-current power supply 210, an inverter circuit 203 connected to the direct-current power supply 210, and a primary coil 205a connected to the inverter circuit 203. The inverter circuit 203 includes capacitors 211, 212, and 213, switching elements 214 and 215 such as FETs, and diodes 214b and 215b. 
The secondary-side circuit includes a secondary coil 205b equipped with a center tap, a rectifier circuit 221 connected to the secondary coil 205b, and a load 209 connected to the rectifier circuit 221. The rectifier circuit 221 includes a load matching capacitor 216, diodes 217 and 218, a current smoothing reactor 219, and a smoothing capacitor 220.
The inverter circuit 203 generates an alternating-current electric signal used for transmitting electric power. The electric signal generated by the inverter circuit 203 is applied to the primary coil 205a. The primary coil 205a and the secondary coil 205b constitute an attachable and detachable transformer 205, and if the primary coil 205a and the secondary coil 205b are situated close to each other, electromagnetic induction is produced between the primary coil 205a and the secondary coil 205b. In addition, the alternating-current electric signal applied to the primary coil 205a is transmitted to the secondary coil 205b using the electromagnetic induction between the primary coil 205a and the secondary coil 205b. The electric signal transmitted to the secondary coil 205b is output to the load 209 after being converted into a direct-current electric signal through the rectifier circuit 221.
In this way, in the non-contact power transfer device 200, electric power is transmitted from the primary-side circuit to the secondary-side circuit in a non-contact manner (wirelessly) using the electromagnetic induction between the primary coil 205a and the secondary coil 205b. 
As a wireless power transmission system of the related art based on the magnetic resonance method, a non-contact power feeding system (a wireless power transmission system) according to Japanese Unexamined Patent Application Publication No. 2010-193598 and so forth have been proposed. FIG. 10 is an explanatory diagram illustrating the configuration of a non-contact power feeding system 300 according to Japanese Unexamined Patent Application Publication No. 2010-193598.
As illustrated in FIG. 10, the non-contact power feeding system 300 includes a power feeding facility 301 (a power transmitting device) and a power receiving device 302. The power feeding facility 301 includes a high-frequency power-supply device 310, a primary coil 320, a primary self-resonance coil 330, and a control device 340. The high-frequency power-supply device 310 generates a predetermined high-frequency voltage, based on a driving signal received from the control device 340, and supplies a high-frequency power used for transmitting electric power. The primary coil 320 transmits, to the primary self-resonance coil 330, the high-frequency power supplied by the high-frequency power-supply device 310. The primary self-resonance coil 330 is an LC resonance coil used for transmitting electric power. C1 is the stray capacitance of the primary self-resonance coil 330.
The power receiving device 302 includes a secondary self-resonance coil 360 and a secondary coil 370. The secondary self-resonance coil 360 is an LC resonance coil for receiving electric power. C2 is the stray capacitance of the secondary self-resonance coil 360. The secondary coil 370 extracts the electric power received by the secondary self-resonance coil 360 and outputs the extracted electric power, to a load 303.
In addition, by using resonance (magnetic resonance) generated between the primary self-resonance coil 330 and the secondary self-resonance coil 360, the non-contact power feeding system 300 transmits electric power from the power feeding facility 301 to the power receiving device 302 in a non-contact manner (wirelessly).
In recent years, there has been a growing need for a wireless power transmission system compatible with two transmission methods such as both the electromagnetic induction method and the magnetic resonance method. In other words, there has been desired practical use of a wireless power transmission system in which electric power can be transmitted from a power transmitting device to a power receiving device even if the power receiving device is a device compatible with any transmission method of the electromagnetic induction method and the magnetic resonance method, or a wireless power transmission system in which electric power can be transmitted from a power transmitting device to a power receiving device even if the power transmitting device is a device compatible with any transmission method of the electromagnetic induction method and the magnetic resonance method.
In addition, in recent years, even in the electromagnetic induction method, a plurality of transmission methods whose transmission frequencies are different have been proposed, and there has been a growing need for a wireless power transmission system compatible with these transmission methods. In the same way, even in the magnetic resonance method, a plurality of transmission methods whose transmission frequencies are different have been proposed, and there has been a growing need for a wireless power transmission system compatible with these transmission methods.
These and other drawbacks exist.